1. Field of the Invention
The present invention relates to an adhesion promoting process for promoting the adhesion of a surface of a substrate, such as a semiconductor wafer or a substrate for forming a LCD, an adhesion promoting device for carrying out the adhesion promoting process, a coating and developing system including the adhesion promoting device, and a storage medium storing a program specifying the steps of the adhesion promoting process.
2. Description of the Related Art
A series of steps of some resist pattern forming process included in a semiconductor device or a LCD substrate fabricating process includes a step of subjecting a substrate, such as a semiconductor wafer (hereinafter, referred to as “wafer”) to an adhesion promoting process. A wafer is processed by the adhesion promoting process to promote the adhesion of a resist film to a base film before coating the wafer with a resist. The adhesion promoting process blows, for example, HMDS (hexamethyldisilazane) vapor against a surface of a wafer for adhesion promotion.
Referring to FIGS. 16A and 16B showing the change of the surface of a wafer W when HMDS gas is blown against the surface of the wafer W, chemical interaction of HMDS molecules and hydroxyl groups on the surface of the wafer W takes place and the hydroxyl groups are replaced with trimethylsilanol groups to make the surface of the wafer W hydrophobic.
In some cases, an immersion exposure is used for forming a resist pattern having lines of a very small width. An immersion exposure process will be briefly described. Operations for forming a transparent liquid film 12 of, for example, pure water between an exposure lens 11 included in an exposure device 1 and a wafer W as shown in FIG. 17A, transversely moving the exposure device 1 to a position corresponding to the next transfer area (shot area) 11A, and exposing the wafer W to light are repeated to transfer a predetermined circuit pattern to a resist film 14. In FIG. 17A, indicated at 13A and 13B are a liquid supply passage and a drainage passage, respectively. The transfer areas 11A are exaggerated. In the immersion exposure process, a resist film 14 formed on the surface of the wafer W is liable to come off because the surface of the wafer W is affected by the liquid flow for forming the liquid film 12. A part of the resist film 14 formed in a beveled peripheral surface of the wafer W is particularly liable to come off. Such peeling of the resist film 14 can be effectively prevented by the adhesion promoting process.
An adhesion promoting device using HMDS includes, for example, a processing vessel defining a processing space and internally provided with a support table for supporting a substrate thereon, a storage tank containing HMDS and connected by a gas supply line to the processing vessel, and an evacuating system for evacuating the processing space. The temperature of the support table can be optionally adjusted to a desired temperature to heat a wafer W. For example, N2 (nitrogen gas) is supplied to the storage tank to vaporize liquid HMDS contained in the storage tank to produce HMDS gas. Nitrogen gas (N2) serves as a carrier gas for carrying HMDS gas through the gas supply line into a space above a central part of the wafer W. Nitrogen gas (N2) can be made to flow together with HMDS gas toward the wafer W or can be made to flow alone toward the wafer W.
An adhesion promoting process to be carried out by the adhesion promoting device will be described with reference to FIGS. 18 and 19. FIG. 18 is a graph showing the variation of the temperatures of the support table and the variation of the temperature of the wafer W by continuous lines and dotted lines, respectively. FIG. 19 shows the change of the surface of the wafer W caused by HMDS molecules 17 carried to the wafer W by N2 flow indicated by thick arrows. Actually, a reaction product is produced by the interaction of HMDS molecules 17 and hydroxyl groups on the wafer W as mentioned above and the reaction product makes the surface of the wafer W hydrophobic. In FIG. 19, the reaction product is represented by the HMDS molecules 17 for convenience.
A wafer W is placed on the support table 18 heated at a temperature between 90° C. and 110° C. at time r1 (FIG. 18) to heat the wafer W from 23° C. corresponding to the temperature of a cleanroom in which, for example, a coating and developing system is installed, to a temperature substantially equal to the temperature of the support table in step Q1 (FIG. 19A). A mixed gas containing N2 and HMDS gas is supplied to a central part of the wafer W and is discharged through a peripheral part of the wafer W so that the mixed gas flows over the entire surface of the wafer W. Consequently, HMDS molecules and hydroxyl groups on the wafer W interact to make the surface of the wafer W hydrophobic. HMDS molecules 17 are attracted to HMDS molecules 17 adhering to the surface of the wafer W by intermolecular force and a molecular layer 19 containing HMDS molecules 17 is formed on the surface of the wafer W as shown in FIG. 19B in step Q2. When the molecular layer 19 is heated, the bond of HMDS molecules 17 forming the molecular layer 19 is weakened by thermal energy. Consequently, some other HMDS molecules 17 are adsorbed by the molecular layer 19, while some of HMDS molecules 17 forming the molecular layer 19 separate from the molecular layer 19.
At time r2, the supply of the mixed gas containing N2 and HMDS gas is stopped and the supply of only N2 is started. Then, N2 flows, similarly to the mixed gas, from a central part toward the circumference of the wafer W. The separation of HMDS molecules 17 from the molecular layer 19, to which HMDS molecules 17 are not supplied anymore, occurs progressively and HMDS molecules 17 separated from the molecular layer 19 are discharged together with N2. Consequently, HMDS molecules 17 in the molecular layer 19 excluding those reacted with the hydroxyl groups in only one lower layer of the molecular layer 19 are removed from the surface of the wafer W as shown in FIG. 19C in step Q3. Consequently, A molecular layer 1A containing HMDS molecules 17 arranged in a single layer is formed as shown in FIG. 19D in step Q4. At time r3, the wafer W is transferred from the support table to a carrying device. A cooling mechanism included in the carrying device cools the wafer W. A time between the times r1 and r2 and a time between the times r2 and r3 are, for example, 30 s and 10 s, respectively. HMDS molecules 17 not reacted with hydroxyl groups and adhering to the wafer W are removed because the free HMDS molecules 17 react with water and reduce the hydrophobic property of the wafer W and to suppress the amine generation of HMDS molecules 17.
Since the resist film is liable to come off the beveled part of the wafer W, the adhesion promoting process needs to spread HMDS gas satisfactorily over the entire surface of the wafer W including the beveled part. Since the wafer W is heated when the mixed gas containing N2 and HMDS gas is supplied to the wafer W to process the wafer W, ascending air currents ascending from the wafer W are produced as indicated by the arrows in FIGS. 19A, 19B, 19C, and 19D. Therefore, the mixed gas needs to be supplied against the ascending air currents. Process gas, such as HMDS gas, tends to flow from a position at a high temperature toward a position at a low temperature. therefore, HMDS molecules 17 are not distributed satisfactorily over the surface of the wafer W heated at the foregoing temperature and hence it is difficult for HMDS molecules 17 to react satisfactorily with the hydroxyl groups on the wafer W. Thus, a large amount of the mixed gas containing N2 and HMDS gas needs to be supplied to process the entire surface including the beveled part of the wafer W uniformly by the adhesion promoting process.
As shown in FIG. 16, the interaction of HMDS molecules 17 and hydroxyl groups on the wafer W produces amine. Similarly, the interaction of HMDS molecules 17 and moisture contained in a processing atmosphere produces amine. Therefore, a large amount of amine is evolved if HMDS gas is supplied at high rates. When a large amount of amine is evolved, amine leaks from the processing vessel into, for example a coating and developing system and it is possible that the leaked amine acts on a resist film formed on a wafer W being carried in the coating and developing system, and deteriorates the quality of the resist to cause defective development. Studies are made to provide an adhesion promoting device using a processing vessel that defines an unsealed processing space into which HMDS gas is supplied to reduce the component parts of the processing vessel, to simplify the construction of the processing vessel and to reduce work for assembling and adjusting the adhesion promoting device. However, it is possible that the use of such a processing vessel defining an unsealed space increases amine leakage. Moreover, the supply of HMDS gas at a high rate increases the cost of the adhesion promoting process.
A technique mentioned in JP-A H7-235084, Paragraph 0026 applies an adhesive to a substrate before coating a surface of the substrate with a resist film. this technique mentions nothing about heating the substrate after that and cannot solve the foregoing problems.